Java-JAVA快速查找多个List中相同的元素

Question

public List getSame(List list1, List list2, List list3) {
        
        List sameList = new ArrayList();
        
        for (int i = 0; i < list1.size(); i++) {
            for (int m = 0; m < list2.size(); m++) {
                if (list1.get(i).equals(list2.get(m))) {
                    for (int n = 0; n < list3.size(); n++) {
                        if (list1.get(i).equals(list3.get(n))) {
                            sameList.add(list1.get(i));
                        }
                    }
                }
            }
        }
        return sameList;
    }

Answer 1

把list的值放到set中，然后set求交集不就ok了吗？

Answer 2

import static org.junit.Assert.*;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

import org.junit.Test;

public class TestXX {

final public <E> List<E> findSameElem(List<List<E>> lists) {
if(lists.size()==0)return Collections.emptyList();
List<E> firstList = lists.get(0);
List<E> tmpList = new ArrayList<>(lists.get(0));
for (int i=1;i<lists.size();i++) {
List<E> aList=lists.get(i);
tmpList.retainAll(aList);
}
return tmpList;
}

@Test
public void testListOfListVersion(){
String[] strs={"23","2312","342","3423","我是谁?", "dfadvav"};
String[] strs1={"23", "我是谁?","dfasd","342","dfadvav"};
String[] strs2={"23","dfasdfad","34d2","我是谁?","dfadvav"};
String[] strsResult={"23","我是谁?","dfadvav"};
List<List<String>> inputList=new ArrayList<>();
inputList.add(Arrays.asList(strs));
inputList.add(Arrays.asList(strs1));
inputList.add(Arrays.asList(strs2));
assertEquals(Arrays.asList(strsResult),
findSameElem(inputList));
}

@SafeVarargs
final public <E> List<E> findSameElem(List<E> firstList, List<E>... lists) {
List<E> tmpList = new ArrayList<>(firstList);
for (List<E> aList: lists) {
tmpList.retainAll(aList);
}
return tmpList;
}

@Test
public void testVarargsVersion(){
String[] strs={"23","2312","342","3423","我是谁?", "dfadvav"};
String[] strs1={"23", "我是谁?","dfasd","342","dfadvav"};
String[] strs2={"23","dfasdfad","34d2","我是谁?","dfadvav"};
String[] strsResult={"23","我是谁?","dfadvav"};
assertEquals(Arrays.asList(strsResult),
findSameElem(Arrays.asList(strs), Arrays.asList(strs1), Arrays.asList(strs2)));
}
}

Java1.7